MAYBE
* Step 1: Failure MAYBE
  + Considered Problem:
      - Strict TRS:
          app(add(n,x),y) -> add(n,app(x,y))
          app(nil(),y) -> y
          head(add(n,x)) -> n
          high(n,add(m,x)) -> if_high(le(m,n),n,add(m,x))
          high(n,nil()) -> nil()
          if_high(false(),n,add(m,x)) -> add(m,high(n,x))
          if_high(true(),n,add(m,x)) -> high(n,x)
          if_low(false(),n,add(m,x)) -> low(n,x)
          if_low(true(),n,add(m,x)) -> add(m,low(n,x))
          if_qs(false(),x,n,y) -> app(quicksort(x),add(n,quicksort(y)))
          if_qs(true(),x,n,y) -> nil()
          isempty(add(n,x)) -> false()
          isempty(nil()) -> true()
          le(0(),y) -> true()
          le(s(x),0()) -> false()
          le(s(x),s(y)) -> le(x,y)
          low(n,add(m,x)) -> if_low(le(m,n),n,add(m,x))
          low(n,nil()) -> nil()
          quicksort(x) -> if_qs(isempty(x),low(head(x),tail(x)),head(x),high(head(x),tail(x)))
          tail(add(n,x)) -> x
      - Signature:
          {app/2,head/1,high/2,if_high/3,if_low/3,if_qs/4,isempty/1,le/2,low/2,quicksort/1,tail/1} / {0/0,add/2
          ,false/0,nil/0,s/1,true/0}
      - Obligation:
          innermost runtime complexity wrt. defined symbols {app,head,high,if_high,if_low,if_qs,isempty,le,low
          ,quicksort,tail} and constructors {0,add,false,nil,s,true}
  + Applied Processor:
      NaturalPI {shape = Mixed 3, restrict = NoRestrict, uargs = UArgs, urules = URules, selector = Nothing}
  + Details:
      Incompatible
MAYBE